System for the automatic filling of earth boreholes with drilling fluid

ABSTRACT

A drilling fluid tank has a float ball therein connected to one end of a flexible cable having a weight on its other end for contacting a pair of electrical switches in response to the movement of the float ball. The cable also has a plurality of spaced triggers for contacting a third switch providing electrical signals indicative of the incremental volumetric flow of mud from the tank into the well bore. Two pairs of solenoid actuated valves are logically responsive to the position of the float ball, to a deadline sensor indicative of hook load and to a paddle sensor located in the drilling fluid return line from the well bore, and automatically control the filling of the tank, the emptying of the tank and the amount of drilling fluid that is allowed to pass into the earth borehole. Electrical circuitry is also provided which measures the amount of fluid passing into the borehole and compares the measured amounts with preselected values and which causes alarms to be activated in the event that the actual fluid volume passing into the well bore falls outside the predetermined values.

United States Patent 1191 Griffin, 111

1451 Sept. 3, 1974 1 SYSTEM FOR THE AUTOMATIC FILLING 0F EARTH BOREl-IOLES WITH DRILLING FLUID [75] Inventor: Phil H. Griffin, III, Houston, Tex.

[73] Assignee: Dresser Industries, Inc., Dallas, Tex.

[22] Filed: June 29, 1973 [21] Appl. No.: 375,261

Related US. Application Data [63] Continuation-in-part of Ser. No. 231,679, March 3,

1972, abandoned.

[52] US. Cl. 175/38, 73/155 [51] Int. Cl E211) 21/04 [58] Field of Search..' 175/24, 25, 38, 48, 65; 73/155 [56] References Cited UNITED STATES PATENTS 3,039,543 6/1962 Loocke 175/38 X 3,324,717 6/1967 B1 55 et a1 175 4 x 3,338,319 8/1967 Griffin, 111 175/25 3,362,487 l/1968 Lindsey 175/38 3,384,178 5/1968 Agnew et al.., 175/25 X 3,422,912 l/1969 Camp 175/48 X 3,605,919 9/1971 Bromell et al. 175/38 X 3,613,806 10/1971 Malott 175/48 3,726,136 4/1973 McKean et al. 73/155 Primary ExaminerHenry C. Sutherland Assistant Examiner-Richard E. Favreau Attorney, Agent, or Firm-John N. l-lazelwood; William E. Johnson, Jr.; Eddie E. Scott [5 7 ABSTRACT A drilling fluid tank has a float ball therein connected to one end of a flexible cable having a weight on its other end for contacting a pair of electrical switches in response to the movement of the float ball. The cable also has a plurality of spaced triggers for contacting a third switch providing electrical signals indicative of the incremental volumetric flow of mud from the tank into the well bore. Two pairs of solenoid actuated valves are logically responsive to the position of the float ball, to a deadline sensor indicative of hook load and to a paddle sensor located in the drilling fluid return line from the well bore, and automatically control the filling of the tank, the emptying of the tank and the amount of drilling fluid that is allowed to pass into the earth borehole. Electrical circuitry is also provided which measures the amount of fluid passing into the borehole and, compares the measured amounts with preselected values and which causes alarms to be activated in the event that the actual fluid volume passing into the well bore falls outside the predetermined values.

5 Claims, 6 Drawing Figures MUD TRIP TANK ELEC- TRONICS PATENTEDSEP 31924 3.833.076

saw u or 4 FIG-.6

SYSTEM FOR THE AUTOMATIC FILLING OF EARTH BOREHOLES WITH DRILLING FLUID RELATED APPLICATION This application is a continuation, at least in part, of my U.S. application Ser. No. 231,679, filed Mar. 3, 1972, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to an improved system for automatically adding drilling fluid to a well bore, and more specifically, to an improved system for automatically adding drilling fluid to a well bore when the level of fluid in the well bore is decreased due to a change in conditions within the well bore.

During drilling operations, it is advantageous to maintain the well bore filled with drilling mud at all times. To maintain such a full hole status, it is necessary to add fluid to the well bore when certain conditions cause a lowering of the fluid level within the well bore. One drilling operation which causes a lowering of the drilling fluid within a well bore is the necessary practice of the pulling of the drill stem from the hole to replace worn drilling bits. When the drill stem is withdrawn from the hole, there is a lowering of the fluid level within the hole caused by absence of the drill stem body which had previously displaced a considerable amount of fluid. The fluid level in a well bore may also be lowered by the filtration of a portion of the liquid into porous formations surrounding the borehole.

A modern drilling operations practice is to maintain, within the borehole, a drilling fluid, commonly referred to as drilling mud, whose hydrostatic head will produce a bottomhole pressure only slightly in excess of the blowout pressures expected to be encountered. It has been found that drilling rates may be increased and mud cost lowered by utilizing such a light drilling mud. When the back pressure held on the formation face by the muds hydrostatic head is further decreased by a lowering of the level of the mud in the well bore, there then exists the danger of the potential blowout. Due to the fact that a well may be more readily killed when the operator has his drill stem near the bottom of the well, it thereby becomes most important to maintain the borehole full when the drill stem is being removed or is completely out of the hole.

Those in the art have attempted to maintain the hole full of drilling fluid by various methods, such as that disclosed in U.S. Pat. No. 3,384,178 which uses a gravitational feed to allow additional drilling fluid to be added to the well bore whenever the fluid within the well bore falls below a predetermined level. Furthermore, it has been known in the art to maintain full hole conditions during withdrawal of the drill stern by having the operator intermittently terminate withdrawal of the pipe and to manually fill the hole, thus producing a considerable waste of rig time. Also, the well may be endangered by the driller miscalculating how often to fill the well bore or by the misfortune of having a less than prudent driller who may completely neglect to fill the hole while removing the drill pipe.

It is therefore the primary object of the invention to provide a new and improved system for automatically maintaining the drilling fluid level within a well borehole;

It is another object of the invention to provide a new I and improved system for maintaining a desired drilling fluid level within a well borehole which is not dependent upon the mud tank being above the desired level within the borehole; and

It is also the object of the invention to provide a new and improved system which monitors the amount of drilling fluid which is automatically pumped into the borehole and which compares this amount with a predetermined volumetric range.

The objects of the invention are accomplished, generally, by the system which automatically fills a drilling fluid tank and which automatically causes the drilling fluid within the tank to be pumped into the well bore in response to a predetermined amount of change in the hook load associated with the drilling operations and which ceases to add drilling fluid to the borehole as an automatic response to the fluid within the well bore achieving a predetermined level.

These and other objects, features and advantages of the invention will be apparent to those skilled in the art by a careful reading of .the following detailed specification and drawing, in which: 7

FIG. 1 is a diagrammatic elevational view of a well drilling rig embodying the present invention, and a schematic illustration of the mud pumping equirnpment and electrical circuits associated therewith;

FIG. 2 is a schematic illustration of bit weight equip ment used with the circuitry according to the present invention;

FIG. 3 is an elevated diagrammatic view of the mud pumping equipment according to the present invention;

FIG. 4 is a schematic illustration of certain switching circuits used with the present invention;

FIG. 5 is a block diagram and schematic illustration of electrical circuitry used with the present invention; and

FIG. 6 is a schematic illustration of additional electrical circuitry used with the present invention.

Referring now to the drawing in more detail, especially to FIG. 1, the well bore 1 having the usual casing 2 contains the drill stem 3 provided at its lower end with a drill bit 4, the stem 3 being turned by a rotary table 5 of the derrick 6. During drilling, drilling mud is pumped from a mud pit 7 by a positive displacement pump 8 (illustrated in FIG. 3) through a mud delivery line 9 and hose 10 into the drill stem 3, being discharged out of the bit 4 into the well bore 1 and returned from the top of casing 2 by a mud return line 11 to the mud pit 7, all in accordance with conventional practice. A manually openable and closable blowout preventer 12 of any suitable conventional type is provided at the upper end of the casing 2.

The derrick 6 is mounted on the platform 13 with its conventional drawworks 14. The drill stem 3 comprises a number of joint sections of pipe terminating in a kelly, a swivel, a hook and a traveling block 15 suspended by a drilling line 16 from a crown block 17. The drawworks 14 also drive a rotary table 5 which in turn transmits the drive to the kelly. One end of the line 16, namely the fast line 16A, is taken to the drawworks 14 which contain the motor or motors for manipulating the drill string.

The other end 168 (called the Deadline) of the drilling line has secured to it an apparatus 18, generally identified by the legend Bit Weight", illustrated in more detail in FIG. 2.

Referring now to FIG. 2, there is illustrated in more detail the Bit Weight apparatus 18. It should be appreciated that this apparatus 18 is for the most part conventional, for example, as described in US. Letters Pat. No. 3,461,978 to F. Whittle, issued Aug. 19, 1969, except for using the electrical signal as is described hereinafter. The lower end of the deadline 16B is secured to an anchorage member 20 including a winding-on drum. A deadline sensor 21 is clamped to the deadline 16B and operates an electrical indicator 22 of the hook load. As is known in the art, Bit Weight is a substractive function arrived at by subtracting the hook load while drilling from the hook load while circulating and rotating while the drill bit is not on the bottom of the hole. As discussed in the aforementioned Whittle patent, the deadline sensor 21 may be of any suitable kind. In this example, the sensor 21 is clamped to the deadline 163 so as to form a kink therein. As the load on the deadline increases, the deadline tends to straighten and thereby actuate the electrical indicator 22. For the purposes of the present invention, the electrical signal from the indicator 22 appearing on the conductor 23 is of the go-no go variety. The conductor 23 is connected to one input of a conventional NAND gate 24, the other input to the NAND gate 24 being from a voltage source, for example, the battery 25. The conductor 26 is connected to the output of the NAND gate 24. It should be appreciated, in the operation of the bit weight apparatus 18, that a signal appears on the conductor 26 only when there is a reduced load on the deadline 168 as indicated by the sensor 21. The conductor 26 is connected to a terminal 27 which is illustrated in detail in FIG. 6.

Referring now to FIG. 3, there is illustrated in more detail the apparatus referred to generally by the numeral 30 in FIG. 1. A positive displacement mud pump 8, conventional in the art, is connected by pipe 31 to a mud pit 7. The mud is pumped from the mud pit 7 to the pipe 9 as previously discussed with respect to FIG. 1. In addition to that system of filling the well bore with mud, the present invention contemplates the use of mud trip tank 32 which is designed primarily to fill the well bore annulus with drilling mud during a drilling trip, i.e., while the driller is removing stands of drill pipe from the drill stem. The trip tank 32 is provided with an overflow outlet 33 and return line 34 for returning drilling mud to the pit 7 whenever the drilling mud reaches a level coinciding with the outlet 33. The lower portion of the trip tank 32 is provided with an outlet 35 which is connected by means of the pipe 36 to the pipe 37 which leads from the mud pit 7. The pipes 36 and 37 are connected to pipe 38 leading to the intake of the conventional mud pump 39 driven by the motor 40.

Located within the pipe 36 is a valve 42 for opening and closing the pipe 36. Located within the pipe 37 is a similar valve 43 for opening and closing the pipe 37. The valves 42 and 43 are conventional and are preferably electrically actuated by a solenoid 44 such that an electrical signal applied to the terminal 45 and electrical conductor 46 between the terminal 45 and the solenoid 44 causes the valve 42 to open and the valve 43 to close. Conversely, the removal of the electrical signal to terminal 45 causes the valve 43 to open and the valve 42 to close.

The output of the mud pump 39 is connected by the pipe 47 to the pipes 48 and 49, the pipe 48 being connected to the top opening 50 in the trip tank 32. The pipe 48 has a valve 51 and the pipe 49 has a valve 52, each of such valves 51 and 52 being designed to open and close the pipes 48 and 49, respectively. As was discussed with respect to the valves 42 and 43 hereinbefore, the valves 51 and 52 are interconnected with an electrically operated solenoid 53 which is connected to the terminal 54 by the electrical conductor 55. In operation, an electrical signal applied to the solenoid 53 causes the valve 51 to close and the valve 52 to open. Conversely, the removal of the signal causes the valve 51 to open and the valve 52 to close.

A pulley 60 is connected to the top of the trip tank 32 and has a flexible tape 61 extending therearound and connected to a float ball 62 floating on the top of the mud 7A in the tank 32. Connected to the outer end of the tape 61 is a weight 63 which is aligned to make contact with the electrical switches 64 and 65 located on the exterior of the tank 32 in response to the movement of the floating ball 62 which moves in conjunction with the varying mud level in the tank 32. The electrical switch 64 is connected to the terminal 66 by an electrical conductor 67. The electrical switch 65 is connected to the terminal 68 by the electrical conductor 69. Also connected to the trip tank 32, connected exteriorly thereto, is an electrical switch 70 which is aligned as to be contacted by a series of evenly spaced triggers 71 which create a series of electrical pulses by way of the conductor 72 to the terminal 73. The switches 64, 65 and 70 are shown in more detail in FIG. 4. The triggers 71 on the tape 61, for example, extrusions or raised portions on the tape, are spaced such that a rise or fall of the float ball 62 creates electrical signals indicative of an increment of rise or fall of a known value, for example, one gallon of fluid in the trip tank 32.

Referring now to FIG. 4, the switches 64, 65 and 70 are illustrated in greater detail. The switches are each spring-loaded to the open position as illustrated and are connected to the batteries 64a, 65a and 70a, respectively. In the operation of switch 70, the triggers 71 on the tape 61 causes the switch 70 to close, thus putting the voltage from battery 70a on the terminal 73. In a similar manner, the weight 63 on tape 61 causes the switches 64 and 65 to be closed as the weight 63 moves down in response to the level of the mud 7a rising in the tank 32, and vice versa.

Referring now to FIG. 5, there is illustrated a circuit a. It should be appreciated that the circuitry 80a of FIG. 5 and 80b of FIG. 6 together comprise the circuit generally identified by the numeral 80 in FIG. 1. The terminal 81 is connected by a conductor 82 (illustrated in FIG. 1) to a paddle switch 83 located in the mud return line 11 (also illustrated in FIG. 1). The paddle switch 83 is a conventional flow sensor having a springloaded or counterweighted paddle interior the pipe 11 to sense the presence of mud flow, if any, in the pipe 1 1. If the flow starts, the paddle moves toward the open end of pipe 11 nearest the mud pit 7. When flow stops, the spring-loaded paddle moves back. An electrical pulse is transmitted along the conductor 82 to indicate mud flow in pipe 11. Connected to the terminal 81 is a switch 84 wherein the electrical signals appearing at 81 may be manually switched either to the junction 101 or the conductor 85.

The terminal 73 is connected by electrical line 86 to a conventional electronic device well known in the art as an exclusive OR" gate 87, the function or which is described hereinafter. Gage 87 can be electromechanical, e.g., through the use of conventional relays, or can employ solid state circuits, whichever is desired by those skilled in the art. I

Gate 87 is operably connected by way of electrical line 88 to a conventional counter 89 which is used for totaling the number of pulses appearing at terminal 73. Suitable counters and commercially available and well known in the art. For example, a suitable counter is the Unipulser, type 49000-405, manufactured by Durant Company of Milwaukee Wisconsin.

Counter 89 is operated by its own voltage source 90 which is connected to counter 89 by way of electrical line 91. A signal from counter 89 actually comes from voltage source 90, not from gate 87, and is passed by electrical line 92 to low set point device 93.

The low set point device 93 is a commercially available and well known device. A suitable device is the Uniset Switch, type 40 500-400, manufactured by Durant Company of Milwaukee, Wisconsin.

Low set point device 93 is operably connected by way of electrical line 94 to a high set point device 95 which can be the same device as device 93 except that it is used to register a maximum number of pulses rather than a minimum number of pulses which is the function of low set point device 93.

Device 93 is also operably connected by way of electrical line 96 to one input of a conventional AND gate 97, the function of which will also be described hereinafter. Gate 97, like gate 87, is a conventional piece of apparatus well known in the art and cam employ either electromechanical relays or solid state circuits as desired.

High set point device 95 is operably connected by way of electrical line 98 to a warning device 99. The output of gate 97 is also operably connected by way of electrical line 100 and terminal 104 to warning device 99.

Warning device 99 can be any device desired such as a horn, whistle, light, and the like.

The switch 84 is connected to terminal 101, which in turn is connected to one of the inputs to gate 87 and also to one of the inputs to gate 97.

The conductor 85 is connected to the timer 102 and through the alternate position of switch 84 to junction 81, the output of timer 102 being connected by way of conductor 103 to the warning device 99. Timer 102 can be any conventional apparatus commercially available and known in the art such as the Time Delay Relay, type TDO-62C30-l A, produced by Guardian of Chicago, Illinois.

Referring now to FIG. 6, the terminal 116 (connected to terminal 81 in FIG. 5) is connected to one side of the coil 117 in relay 118, the other side of which is grounded. The terminal 68 is connected to one side of the coil 119 of relay 120, the other side of which is grounded. The terminal 68 is also connected to the normally closed contact 121 of relay 118. The terminal 45 is connected to the wiper arm 122 of relay 120 and the normally open contact 123 associated with wiper arm 122 is connected to the positive side of battery 124, the negative side of battery 124 being grounded. Terminal 66 is connected to one side of the coil 109 of relay 1 10,

the other side of which is grounded. The wiper arm 112 of relay associated with the normally closed contact 111 is connected to wiper arm 134 of relay 118. The normally closed contact 111 of relay 110 is connected to wiper arm 133 of relay 129. The wiper arm 1 14 of relay 110 associated with the normally closed contact 113 is connected to wiper arm 126 of relay 118 associated with the normally closed contact 121. The wiper arm 125 of relay is connected to the normally closed contact 1 13 of relay 110. The normally open contact 127 of relay 120 associated with wiper arm is connected to the positive side of battery 124. Terminal 27 is connected to one side of the coil 128 of relay 129, the other side of the coil being grounded. Terminal 54 is connected to the wiper arm 130 of relay 129, the normally open contact 131 associated with wiper arm 130 being connected to the positive side of battery 124 and also to the normally open contact 132 associated with the wiper arm 133 of relay 129. The normally closed contact associated with wiper arm 134 of relay 118 is also connected to terminal 27.

In the operation of the circuitry and apparatus hereinbefore described in detail, after the driller determines to make a trip, he presets, within a given range as determined by the high and low set points, into the pump stroke counting-and alarm device illustrated in FIG. 5 the number of gallons required to refill the hole after each single 90 foot stand is pulled from the hole. The counting system within the counting and alarm device of FIG. 5 is nearly identical to that described and disclosed in U.S. Pat. No. 3,614,761 to W. A. Rehm, et al, assigned to the assignee of the present application. The disclosure of that patent is incorporated herein by reference except to the extent as it is modified and shown to be different as set forth hereinafter. As set forth in the disclosure of such previous patent, if an insufficient quantity of fluid causes flow from the well bore, an alarm will be given signifying gain and should the hole require an excess of fluid an alarm will be given signifying fluid loss. After the presetting step, the driller will then energize motor 40 (FIG. 3) causing the mud pump 39 to circulate drilling fluid. Drilling fluid is withdrawn from pit 7 through line 37, valve 43 and into the suction of the mud pump 39. The discharge from pump 39 passes through line 47, valve 51 and discharges through outlet 50 into the trip tank 32. Valves 42 and 52 are closed. By running the mud pump 39 at a high flow rate, the trip tank 32 can be filled very rapidly. When the fluid level in the trip tank 32 reaches the level of the outlet port 33, excess fluid overflows through line 34 and returns into the mud pit 7. Float ball 62 will have been rising along with the fluid level in the trip tank 32. The float ball 62 is connected to a flexible cable 61 which passes over the pulley 60. The triggers 71 positioned on the flexible cable 61 are so positioned as to strike the switch 70 as the cable is pulled across the pulley 60. By properly spacing the distance between the triggers 71, it is possible to calibrate the system in such a manner that a rise or fall of the float ball 62 causes the switch 70 to open or close in response to an increment of rise or fall equal to a given volumetric increment, for example, one gallon of fluid in the trip tank 32. The switch 70 is connected to the terminal 73 in FIGS. 3 and 5. In FIG. 5 it is seen that an electrical impulse appearing at terminal 73 thus delivers a signal to the exclusive OR gate 87.

Referring again to FIG. 3, when the float ball 62 reaches the level of the outlet port 33, the weight 63 contacts the switch 65, thus causing the voltage from battery 65a to appear at terminal 68. This voltage activates the relay 120 (see FIG. 6) and causes the voltage from battery 124 to be applied to the junction 45. The wiper arm 125 and normally open terminal 127 and wiper arm 114 and normally closed contact 113 of relay 110 are used to cause the relay 120 to lock up until deactivated as explained hereinafter. When the voltage from the battery 124 is applied to the terminal 45, this voltage is then applied to the solenoid 44 in FIG. 3. This causes the valve 43 to close and the valve 42 to open. With the valves 42 and 43 so positioned, fluid is drawn from the trip tank 32 through valve 42 into the mud pump 39 and discharged through line 47 and valve 51 to the trip tank 32. While this might appear at first glance to be wasted motion, this feature enables the mud pump to run continuously.

While the trip tank 32 has been automatically filling to a predetermined level, the driller will have been withdrawing one stand of drill pipe from the well bore causing the fluid level within the borehole to drop from the level 141 to the level 142, illustrated in FIG. 1. In order to disconnect the removed stand of drill pipe from the remainder of the drill pipe in the well bore, it is necessary that the driller set the drill stem in the slips. This removes the weight of all the drill pipe remaining in the well bore from the block 15. The removal of this weight signifies that a stand of drill pipe has been removed from the well bore and pipe will not again be removed until this particular stand has been unscrewed and placed in the pipe rack (not illustrated). The switch 21 in FIG. 2 on the deadline" 16b of the drilling rig senses the reduction in weight on the hook and transfers a signal from the NAND gate 24 of the junction 27. to

Referring now to FIG. 6, a signal appearing at the junction 27 energizes the relay 129 causing the voltage from battery 124 appear at terminal 54. It should also be appreciated that the relay 129 is locked up in this position through the action of the wiper arm 133 and the normally open contact 132 associated therewith and the wiper arm 112 and normally closed contact 1 11 of relay 110. The voltage appearing at the terminal 54 is then applied to the solenoid 53 illustrated in FIG. 3 to close the valve 51 and open the valve 52. With the valves 51 and 52 in this position, the drilling fluid is drawn from the trip tank 32 through valve 42 into the pump 39, discharged through the line 47 and valve 52 into the line 49. From the line 49, the drilling mud is pumped into the well bore 1, thus causing the fluid level to return to the level 141 (see FIG. 1). When the mud level reaches the level 141, it flows through pipe 11 and contacts the paddle switch 83, thus causing an electric signal to be sent along the conductor 82. This same electrical signal thus appears at the junction 81, illustrated in FIGS. 3 and 5. In FIG. 5, it is seen that the electrical signal appearing at terminal 81 causes a signal to appear at junction 101 and to be coupled into the exclusive OR gate 87. If the exclusive OR gate 87 receives a signal from the junction 101, the gate 87 ceases to pass signals from the input terminal 73 (indicative of the triggers 71 contacting the switch 70 in FIG. 3) and thereby stops the action of the counter 89. Thus, the gate 87 will pass signals received from the junction 73 as long as no signal is also received from the flow paddle 83.

In the alternate position of the switch 84, the signal appearing at terminal 81 is passed to the timer 102. By setting the timer at any desired time delay, for example, zero, 30 seconds or 1 minute, the action of the paddle switch 83 can thus activate the alarm 99.

As shown in FIG. 5, the signal appearing at junction 81 is also coupled into junction 116 by the conductor 141. In FIG. 6, the junction 116 is illustrated as being connected to the coil 117 of the relay 118. Thus, a signal appearing at terminal 116, being indicative of the activation of the paddle switch 83, activates relay 118 and thus defeats the lockup action of the relays 120 and 129. This in turn causes solenoids 44 and 53 to be deactivated, thus causing valves 42 and 52 to be closed and valves 43 and 51 to opened, thereby allowing the starting point for the process to commence again whereby the trip tank is automatically refilled as described above.

During the period of time when the valves 42 and 52 are open and the valves 51 and 43 are closed, the fluid is pumped from the trip tank 32 into the well bore. As the fluid level drops due to removal of fluid from the tank 32, the float ball 62 follows the mud level down. The line 61 passing over the pulley 60 responds to the level change of the float ball 62 and causes the triggers 71 to successively activate the switch 70. Each of these switch closures causes the counter 89 to record that a single increment, for example, 1 gallon, has passed from the trip tank 32 into the well bore. This count will continue until the fluid level in the well bore is restored to the level 141 and the count is stopped by motion of the paddle 83. The circuitry of FIG. 5 automatically compares the volume of fluid pumped into the well bore against the preset values and causes an alarm should the preset values and actual values be out of agreement. Should the hole be losing circulation and accept all of fluid from trip tank 32 without becoming full, the weight 63 contacts the switch 64, causing an electrical signal to appear at junction 66. As seen in FIG. 6, this signal activates the relay 1 10, thus unlocking the lockup features of the relays 120 and 129, and causing the trip tank 32 to begin the refill cycle.

It should be appreciated that the apparatus and circuitry as described herein is entirely automatic and is controlled by the position of the float ball 62, the deadline sensor 21 and the paddle 83. It should also be appreciated that while the process has been described as being useful while pulling pipe, the fluid displaced from the well bore by the re-insertion of the drill pipe during a trip into the hole can also be measured and compared against preset values. The use of this device and the proper weighting of predetermined values prevents the intrusion of formation fluid or the loss of drilling fluid with respect to the well bore by giving further an alarm. It should also be appreciated by those skilled in the art that while the preferred embodiments of the present invention have been described and illustrated herein, the signals and response mechanisms may alternately be pneumatic, fluidic, hydraulic, mechanical or combinations thereof to accomplish the purposes and objects of this invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In the apparatus for drilling a well in which casing extends down the well, drill pipe extends down the well within the casing, and drilling fluid is circulated from a drilling fluid tank into the annulus between the drill pipe and the casing and discharged from the well through a drilling fluid return line, the improvement comprising:

means for filling said drilling fluid tank to a predetermined first level;

means for discharging the drilling fluid from said tank into the annulus in response to the occurrence of a predetermined event associated with the drilling operation which is independent of the level of the drilling fluid in the annulus; and

means for disablingsaid discharge means in response to said drilling fluid reaching a predetermined level in the annulus of said well.

2. In the apparatus for drilling a well in which casing extends down the well, drill pipe extends down the well within the casing, and drilling fluid is circulated from a drilling fluid tank into the annulus between the drill pipe and the casing and discharged from the well through a drilling fluid return line, the improvement comprising:

means for filling said drilling fluid tank to a predetermined first level;

means for discharging the drilling fluid from said tank into the annulus in response to a predetermined amount of change in the hook load associated with said drill pipe; and means for disabling said discharge means in response to said drilling fluid reaching a predetermined level in the annulus of said well. 3. In the apparatus according to claim 2, the improvement additionally comprising:

means for generating a series of signals indicative of volumetric fluid changes in said drilling fluid tank; and means for comparing at least a portion of said signals with predetermined minimum and maximum signals, whereby the fluid loss or gain in the well is determined. 4. In the apparatus according to claim 2, the improvement additionally comprising:

second means for disabling said discharge means in response to the drilling fluid in said tank reaching a second predetermined level before the fluid reaches said predetermined level in the annulus of said well. 5. In the apparatus according to claim 4, the improvement additionally comprising:

means for refilling said drilling fluid tank to establish the normal sequence of events. 

1. In the apparatus for drilling a well in which casing extends down the well, drill pipe extends down the well within the casing, and drilling fluid is circulated from a drilling fluid tank into the annulus between the drill pipe and the casing and discharged from the well through a drilling fluid return line, the improvement comprising: means for filling said drilling fluid tank to a predetermined first level; means for discharging the drilling fluid from said tank into the annulus in response to the occurrence of a predetermined event associated with the drilling operation which is independent of the level of the drilling fluid in the annulus; and means for disabling said discharge means in response to said drilling fluid reaching a predetermined level in the annulus of said well.
 2. In the apparatus for drilling a well in which casing extends down the well, drill pipe extends down the well within the casing, and drilling fluid is circulated from a drilling fluid tank into the annulus between the drill pipe and the casing and discharged from the well through a drilling fluid return line, the improvement comprising: means for filling said drilling fluid tank to a predetermined first level; means for discharging the drilling fluid from said tank into the annulus in response to a predetermined amount of change in the hook load associated with said drill pipe; and means for disabling said discharge means in response to said drilling fluid reaching a predetermined level in the annulus of said well.
 3. In the apparatus according to claim 2, the improvement additionally comprising: means for generating a series of signals indicative of volumetric fluid changes in said drilling fluid tank; and means for comparing at least a portion of said signals with predetermined minimum and maximum signals, whereby the fluid loss or gain in the well is determined.
 4. In the apparatus according to claim 2, the improvement additionally comprising: second means for disabling said discharge means in response to the drilling fluid in said tank reaching a second predetermined level before the fluid reaches said predetermined level in the annulus of said well.
 5. In the aPparatus according to claim 4, the improvement additionally comprising: means for refilling said drilling fluid tank to establish the normal sequence of events. 